The deal is only around for a limited time and is good through Sunday, September, 28, 2014.
In my area, it's not that great a deal as they also offer a deal where you can get a large, 1-topping pizza for $10 and a large, 5-topping pizza for $12.
Not too long ago, they were offering any large for $10, but with food prices going up, it looks like even the pizza chains are scaling back. Even Domino's medium, 2-topping Handmade Pan Pizza went up by a buck to $8.99 this year!